Field of the Invention
The present invention relates to a flexible organic light emitting display. More particularly, the present invention relates to a flexible organic light emitting display that includes a thin film transistor (TFT) driving device formed on an ultra-thin film glass substrate and an organic light emitting element, and a method of fabricating the same.
Discussion of the Related Art
An organic light emitting display (OLED) is a self-light emitting display device, and may be fabricated to have a lightweight and slim size because it does not need a separate light source, as in a liquid crystal display (LCD). Also, the organic light emitting display is favorable with respect to power consumption due to low driving voltage and also is excellent for color realization, response speed, viewing angle, and contrast ratio (CR). As a result, the organic light emitting display has been studied as a next-generation display.
Particularly, studies of a flexible organic light emitting display (flexible OLED), which may be bent or unbent, or may be folded or unfolded, so as to be used for various applications, have been actively made. In case of such a flexible organic light emitting display, a plastic based substrate such as polyimide (PI) may be used to realize a flexible substrate.
Since the organic light emitting display uses an organic material which is a compound of a conjugated molecular structure as a light emitting layer, a serious problem occurs in that the organic light emitting layer is highly sensitive to oxygen and water. Thus, deteriorating the device. Deterioration of the organic light emitting layer due to oxygen and water could lead to deterioration of lifetime of the organic light emitting display. For this reason, the organic light emitting display should encapsulate the organic light emitting element that includes the organic light emitting layer. At this time, in order that deterioration caused by oxygen and water of the organic light emitting layer does not cause a defect of the organic light emitting display, it is known that a water vapor transmission rate (WVTR) value of an encapsulation member should be 10-6 g/m2·day or less. That is, it is known that a barrier characteristic level required by the organic light emitting display has a WVTR value of 10-6 g/m2·day or less. To this end, the organic light emitting element is protected by a substrate having a low WVTR value or an encapsulation member of various materials.
However, the plastic based substrate used to realize the flexible organic light emitting display has a WVTR value that is relatively higher than that of a glass substrate having a perfect WVTR characteristic. That is, oxygen and water do not pass through the glass substrate, whereas oxygen and water could pass through the plastic based substrate relatively easily. Therefore, if the organic light emitting display is fabricated using the plastic based substrate, oxygen and water are easily permeated into the organic light emitting element. This becomes the most important defect factor in the organic light emitting display that uses a plastic based substrate.
Therefore, efforts for solving water permeation in a plastic substrate based flexible organic light emitting display have been made in such a manner that barrier layers, which are bendable while preventing oxygen and water from being permeated between organic light emitting element including an organic light emitting layer and an upper substrate and between the organic light emitting element and a lower substrate, are formed. One of the efforts is a thin film encapsulation technique that alternately deposits an inorganic film and an organic film on the organic light emitting element that includes the organic light emitting layer. For example, a technique of the Korean Patent Application No. 10-2011-0101016 has been provided, in which a multi-buffer layer is provided between an organic light emitting layer and a plastic based substrate and has a structure that an inorganic layer of SiOx and an inorganic layer of SiNx are deposited alternately.